1 /* 2 * Copyright (C) 2008 IBM Corporation 3 * Author: Mimi Zohar <zohar@us.ibm.com> 4 * 5 * This program is free software; you can redistribute it and/or modify 6 * it under the terms of the GNU General Public License as published by 7 * the Free Software Foundation, version 2 of the License. 8 * 9 * ima_policy.c 10 * - initialize default measure policy rules 11 * 12 */ 13 #include <linux/module.h> 14 #include <linux/list.h> 15 #include <linux/security.h> 16 #include <linux/magic.h> 17 #include <linux/parser.h> 18 19 #include "ima.h" 20 21 /* flags definitions */ 22 #define IMA_FUNC 0x0001 23 #define IMA_MASK 0x0002 24 #define IMA_FSMAGIC 0x0004 25 #define IMA_UID 0x0008 26 27 enum ima_action { UNKNOWN = -1, DONT_MEASURE = 0, MEASURE }; 28 29 #define MAX_LSM_RULES 6 30 enum lsm_rule_types { LSM_OBJ_USER, LSM_OBJ_ROLE, LSM_OBJ_TYPE, 31 LSM_SUBJ_USER, LSM_SUBJ_ROLE, LSM_SUBJ_TYPE 32 }; 33 34 struct ima_measure_rule_entry { 35 struct list_head list; 36 enum ima_action action; 37 unsigned int flags; 38 enum ima_hooks func; 39 int mask; 40 unsigned long fsmagic; 41 uid_t uid; 42 struct { 43 void *rule; /* LSM file metadata specific */ 44 int type; /* audit type */ 45 } lsm[MAX_LSM_RULES]; 46 }; 47 48 /* 49 * Without LSM specific knowledge, the default policy can only be 50 * written in terms of .action, .func, .mask, .fsmagic, and .uid 51 */ 52 53 /* 54 * The minimum rule set to allow for full TCB coverage. Measures all files 55 * opened or mmap for exec and everything read by root. Dangerous because 56 * normal users can easily run the machine out of memory simply building 57 * and running executables. 58 */ 59 static struct ima_measure_rule_entry default_rules[] = { 60 {.action = DONT_MEASURE,.fsmagic = PROC_SUPER_MAGIC,.flags = IMA_FSMAGIC}, 61 {.action = DONT_MEASURE,.fsmagic = SYSFS_MAGIC,.flags = IMA_FSMAGIC}, 62 {.action = DONT_MEASURE,.fsmagic = DEBUGFS_MAGIC,.flags = IMA_FSMAGIC}, 63 {.action = DONT_MEASURE,.fsmagic = TMPFS_MAGIC,.flags = IMA_FSMAGIC}, 64 {.action = DONT_MEASURE,.fsmagic = SECURITYFS_MAGIC,.flags = IMA_FSMAGIC}, 65 {.action = DONT_MEASURE,.fsmagic = SELINUX_MAGIC,.flags = IMA_FSMAGIC}, 66 {.action = MEASURE,.func = FILE_MMAP,.mask = MAY_EXEC, 67 .flags = IMA_FUNC | IMA_MASK}, 68 {.action = MEASURE,.func = BPRM_CHECK,.mask = MAY_EXEC, 69 .flags = IMA_FUNC | IMA_MASK}, 70 {.action = MEASURE,.func = PATH_CHECK,.mask = MAY_READ,.uid = 0, 71 .flags = IMA_FUNC | IMA_MASK | IMA_UID}, 72 }; 73 74 static LIST_HEAD(measure_default_rules); 75 static LIST_HEAD(measure_policy_rules); 76 static struct list_head *ima_measure; 77 78 static DEFINE_MUTEX(ima_measure_mutex); 79 80 static bool ima_use_tcb __initdata; 81 static int __init default_policy_setup(char *str) 82 { 83 ima_use_tcb = 1; 84 return 1; 85 } 86 __setup("ima_tcb", default_policy_setup); 87 88 /** 89 * ima_match_rules - determine whether an inode matches the measure rule. 90 * @rule: a pointer to a rule 91 * @inode: a pointer to an inode 92 * @func: LIM hook identifier 93 * @mask: requested action (MAY_READ | MAY_WRITE | MAY_APPEND | MAY_EXEC) 94 * 95 * Returns true on rule match, false on failure. 96 */ 97 static bool ima_match_rules(struct ima_measure_rule_entry *rule, 98 struct inode *inode, enum ima_hooks func, int mask) 99 { 100 struct task_struct *tsk = current; 101 int i; 102 103 if ((rule->flags & IMA_FUNC) && rule->func != func) 104 return false; 105 if ((rule->flags & IMA_MASK) && rule->mask != mask) 106 return false; 107 if ((rule->flags & IMA_FSMAGIC) 108 && rule->fsmagic != inode->i_sb->s_magic) 109 return false; 110 if ((rule->flags & IMA_UID) && rule->uid != tsk->cred->uid) 111 return false; 112 for (i = 0; i < MAX_LSM_RULES; i++) { 113 int rc = 0; 114 u32 osid, sid; 115 116 if (!rule->lsm[i].rule) 117 continue; 118 119 switch (i) { 120 case LSM_OBJ_USER: 121 case LSM_OBJ_ROLE: 122 case LSM_OBJ_TYPE: 123 security_inode_getsecid(inode, &osid); 124 rc = security_filter_rule_match(osid, 125 rule->lsm[i].type, 126 Audit_equal, 127 rule->lsm[i].rule, 128 NULL); 129 break; 130 case LSM_SUBJ_USER: 131 case LSM_SUBJ_ROLE: 132 case LSM_SUBJ_TYPE: 133 security_task_getsecid(tsk, &sid); 134 rc = security_filter_rule_match(sid, 135 rule->lsm[i].type, 136 Audit_equal, 137 rule->lsm[i].rule, 138 NULL); 139 default: 140 break; 141 } 142 if (!rc) 143 return false; 144 } 145 return true; 146 } 147 148 /** 149 * ima_match_policy - decision based on LSM and other conditions 150 * @inode: pointer to an inode for which the policy decision is being made 151 * @func: IMA hook identifier 152 * @mask: requested action (MAY_READ | MAY_WRITE | MAY_APPEND | MAY_EXEC) 153 * 154 * Measure decision based on func/mask/fsmagic and LSM(subj/obj/type) 155 * conditions. 156 * 157 * (There is no need for locking when walking the policy list, 158 * as elements in the list are never deleted, nor does the list 159 * change.) 160 */ 161 int ima_match_policy(struct inode *inode, enum ima_hooks func, int mask) 162 { 163 struct ima_measure_rule_entry *entry; 164 165 list_for_each_entry(entry, ima_measure, list) { 166 bool rc; 167 168 rc = ima_match_rules(entry, inode, func, mask); 169 if (rc) 170 return entry->action; 171 } 172 return 0; 173 } 174 175 /** 176 * ima_init_policy - initialize the default measure rules. 177 * 178 * ima_measure points to either the measure_default_rules or the 179 * the new measure_policy_rules. 180 */ 181 void __init ima_init_policy(void) 182 { 183 int i, entries; 184 185 /* if !ima_use_tcb set entries = 0 so we load NO default rules */ 186 if (ima_use_tcb) 187 entries = ARRAY_SIZE(default_rules); 188 else 189 entries = 0; 190 191 for (i = 0; i < entries; i++) 192 list_add_tail(&default_rules[i].list, &measure_default_rules); 193 ima_measure = &measure_default_rules; 194 } 195 196 /** 197 * ima_update_policy - update default_rules with new measure rules 198 * 199 * Called on file .release to update the default rules with a complete new 200 * policy. Once updated, the policy is locked, no additional rules can be 201 * added to the policy. 202 */ 203 void ima_update_policy(void) 204 { 205 const char *op = "policy_update"; 206 const char *cause = "already exists"; 207 int result = 1; 208 int audit_info = 0; 209 210 if (ima_measure == &measure_default_rules) { 211 ima_measure = &measure_policy_rules; 212 cause = "complete"; 213 result = 0; 214 } 215 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL, 216 NULL, op, cause, result, audit_info); 217 } 218 219 enum { 220 Opt_err = -1, 221 Opt_measure = 1, Opt_dont_measure, 222 Opt_obj_user, Opt_obj_role, Opt_obj_type, 223 Opt_subj_user, Opt_subj_role, Opt_subj_type, 224 Opt_func, Opt_mask, Opt_fsmagic, Opt_uid 225 }; 226 227 static match_table_t policy_tokens = { 228 {Opt_measure, "measure"}, 229 {Opt_dont_measure, "dont_measure"}, 230 {Opt_obj_user, "obj_user=%s"}, 231 {Opt_obj_role, "obj_role=%s"}, 232 {Opt_obj_type, "obj_type=%s"}, 233 {Opt_subj_user, "subj_user=%s"}, 234 {Opt_subj_role, "subj_role=%s"}, 235 {Opt_subj_type, "subj_type=%s"}, 236 {Opt_func, "func=%s"}, 237 {Opt_mask, "mask=%s"}, 238 {Opt_fsmagic, "fsmagic=%s"}, 239 {Opt_uid, "uid=%s"}, 240 {Opt_err, NULL} 241 }; 242 243 static int ima_lsm_rule_init(struct ima_measure_rule_entry *entry, 244 char *args, int lsm_rule, int audit_type) 245 { 246 int result; 247 248 entry->lsm[lsm_rule].type = audit_type; 249 result = security_filter_rule_init(entry->lsm[lsm_rule].type, 250 Audit_equal, args, 251 &entry->lsm[lsm_rule].rule); 252 return result; 253 } 254 255 static int ima_parse_rule(char *rule, struct ima_measure_rule_entry *entry) 256 { 257 struct audit_buffer *ab; 258 char *p; 259 int result = 0; 260 261 ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_INTEGRITY_RULE); 262 263 entry->action = -1; 264 while ((p = strsep(&rule, " \n")) != NULL) { 265 substring_t args[MAX_OPT_ARGS]; 266 int token; 267 unsigned long lnum; 268 269 if (result < 0) 270 break; 271 if (!*p) 272 continue; 273 token = match_token(p, policy_tokens, args); 274 switch (token) { 275 case Opt_measure: 276 audit_log_format(ab, "%s ", "measure"); 277 entry->action = MEASURE; 278 break; 279 case Opt_dont_measure: 280 audit_log_format(ab, "%s ", "dont_measure"); 281 entry->action = DONT_MEASURE; 282 break; 283 case Opt_func: 284 audit_log_format(ab, "func=%s ", args[0].from); 285 if (strcmp(args[0].from, "PATH_CHECK") == 0) 286 entry->func = PATH_CHECK; 287 else if (strcmp(args[0].from, "FILE_MMAP") == 0) 288 entry->func = FILE_MMAP; 289 else if (strcmp(args[0].from, "BPRM_CHECK") == 0) 290 entry->func = BPRM_CHECK; 291 else 292 result = -EINVAL; 293 if (!result) 294 entry->flags |= IMA_FUNC; 295 break; 296 case Opt_mask: 297 audit_log_format(ab, "mask=%s ", args[0].from); 298 if ((strcmp(args[0].from, "MAY_EXEC")) == 0) 299 entry->mask = MAY_EXEC; 300 else if (strcmp(args[0].from, "MAY_WRITE") == 0) 301 entry->mask = MAY_WRITE; 302 else if (strcmp(args[0].from, "MAY_READ") == 0) 303 entry->mask = MAY_READ; 304 else if (strcmp(args[0].from, "MAY_APPEND") == 0) 305 entry->mask = MAY_APPEND; 306 else 307 result = -EINVAL; 308 if (!result) 309 entry->flags |= IMA_MASK; 310 break; 311 case Opt_fsmagic: 312 audit_log_format(ab, "fsmagic=%s ", args[0].from); 313 result = strict_strtoul(args[0].from, 16, 314 &entry->fsmagic); 315 if (!result) 316 entry->flags |= IMA_FSMAGIC; 317 break; 318 case Opt_uid: 319 audit_log_format(ab, "uid=%s ", args[0].from); 320 result = strict_strtoul(args[0].from, 10, &lnum); 321 if (!result) { 322 entry->uid = (uid_t) lnum; 323 if (entry->uid != lnum) 324 result = -EINVAL; 325 else 326 entry->flags |= IMA_UID; 327 } 328 break; 329 case Opt_obj_user: 330 audit_log_format(ab, "obj_user=%s ", args[0].from); 331 result = ima_lsm_rule_init(entry, args[0].from, 332 LSM_OBJ_USER, 333 AUDIT_OBJ_USER); 334 break; 335 case Opt_obj_role: 336 audit_log_format(ab, "obj_role=%s ", args[0].from); 337 result = ima_lsm_rule_init(entry, args[0].from, 338 LSM_OBJ_ROLE, 339 AUDIT_OBJ_ROLE); 340 break; 341 case Opt_obj_type: 342 audit_log_format(ab, "obj_type=%s ", args[0].from); 343 result = ima_lsm_rule_init(entry, args[0].from, 344 LSM_OBJ_TYPE, 345 AUDIT_OBJ_TYPE); 346 break; 347 case Opt_subj_user: 348 audit_log_format(ab, "subj_user=%s ", args[0].from); 349 result = ima_lsm_rule_init(entry, args[0].from, 350 LSM_SUBJ_USER, 351 AUDIT_SUBJ_USER); 352 break; 353 case Opt_subj_role: 354 audit_log_format(ab, "subj_role=%s ", args[0].from); 355 result = ima_lsm_rule_init(entry, args[0].from, 356 LSM_SUBJ_ROLE, 357 AUDIT_SUBJ_ROLE); 358 break; 359 case Opt_subj_type: 360 audit_log_format(ab, "subj_type=%s ", args[0].from); 361 result = ima_lsm_rule_init(entry, args[0].from, 362 LSM_SUBJ_TYPE, 363 AUDIT_SUBJ_TYPE); 364 break; 365 case Opt_err: 366 audit_log_format(ab, "UNKNOWN=%s ", p); 367 break; 368 } 369 } 370 if (entry->action == UNKNOWN) 371 result = -EINVAL; 372 373 audit_log_format(ab, "res=%d", !result ? 0 : 1); 374 audit_log_end(ab); 375 return result; 376 } 377 378 /** 379 * ima_parse_add_rule - add a rule to measure_policy_rules 380 * @rule - ima measurement policy rule 381 * 382 * Uses a mutex to protect the policy list from multiple concurrent writers. 383 * Returns 0 on success, an error code on failure. 384 */ 385 int ima_parse_add_rule(char *rule) 386 { 387 const char *op = "update_policy"; 388 struct ima_measure_rule_entry *entry; 389 int result = 0; 390 int audit_info = 0; 391 392 /* Prevent installed policy from changing */ 393 if (ima_measure != &measure_default_rules) { 394 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL, 395 NULL, op, "already exists", 396 -EACCES, audit_info); 397 return -EACCES; 398 } 399 400 entry = kzalloc(sizeof(*entry), GFP_KERNEL); 401 if (!entry) { 402 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL, 403 NULL, op, "-ENOMEM", -ENOMEM, audit_info); 404 return -ENOMEM; 405 } 406 407 INIT_LIST_HEAD(&entry->list); 408 409 result = ima_parse_rule(rule, entry); 410 if (!result) { 411 mutex_lock(&ima_measure_mutex); 412 list_add_tail(&entry->list, &measure_policy_rules); 413 mutex_unlock(&ima_measure_mutex); 414 } else { 415 kfree(entry); 416 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL, 417 NULL, op, "invalid policy", result, 418 audit_info); 419 } 420 return result; 421 } 422 423 /* ima_delete_rules called to cleanup invalid policy */ 424 void ima_delete_rules(void) 425 { 426 struct ima_measure_rule_entry *entry, *tmp; 427 428 mutex_lock(&ima_measure_mutex); 429 list_for_each_entry_safe(entry, tmp, &measure_policy_rules, list) { 430 list_del(&entry->list); 431 kfree(entry); 432 } 433 mutex_unlock(&ima_measure_mutex); 434 } 435